BitLocker recovery key
The BitLocker recovery key is a unique 48-digit numeric password that you can use to unlock your system. The recovery key is generated when BitLocker is enabled on a system and the data carrier is encrypted. The BitLocker setup process forces the creation of a recovery key at the time of activation and cannot be bypassed.
When is the recovery key required?
The recovery key is required and is requested by Windows as soon as an unsafe condition is detected. Some hardware, firmware or software changes may present conditions in which Windows requires you to enter a recovery key. In this case it is used to decrypt the data carrier without enabling by a TPM.
Further Information